Aircraft antenna



June 13, 1950 D. H. MITCHELL AIRCRAFT ANTENNA 2 Sheets-Sheet 2 Filed Aug. 17, 1945 INVENTOR.

Don 0w MITCHELL 8W3 Ni 3 NM Patented June 13, 1950 AIRCRAFT ANTENNA Donald H. Mitchell, Chicago, 111., assignor to Motorola, Inc., a corporation of Illinois Application August 17, 1945, Serial No. 611,183

12 Claims.

The present invention relates to aircraft antennas and more particularly to improved apparatus for automatically extending and retracting an aircraft antenna.

For long range radio transmission and reception aboard an aircraft, it has heretofore been conventional practice to utilize an antenna wire of considerable length which is reeled out after the craft attains a safe flying altitude and is reeled in before landing the craft. Usually, the reeling operations are performed manually, although various manually controlled motor or hydraulic powered mechanisms have been proposed for this purpose. When landing a craft, the pilots attention is fully occupied with many operating details other than that of reeling in the antenna wire, with the result that the reeling operation is sometimes forgotten and the antenna wire is broken during the landing operation.

It is an object of the present invention, therefore, to provide a self-extending and retracting antenna, system for an aircraft which functions entirely automatically without any attention from the craft operator.

According to another object of the invention, the differential speed between the landing and normal flying speeds of the craft is relied upon automatically to effect extension and retraction of the antenna element.

It is another object of the invention to provide an antenna system of the character described which is of simple, rugged and economical construction, and is completely reliable in operation.

It is a further object of the invention to provide an aircraft antenna of the character described in which an antenna extension greatly in excess of the retracted antenna length may be obtained.

It is still another object of the invention to provide in an antenna system of the character described, facilities for automatically controlling the tuning of the antenna circuit as the antenna is extended and retracted.

The invention, both as to its organization and method of operation, together wtih further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which:

Fig. l is a perspective view of a small aircraft equipped with one embodiment of the present improved antenna;

Fig. 2 is a fragmentary side view partially in section of the antenna shown in Fig. 1;

Fig. 3 is a side view partially in section illustrating a modified embodiment of the invention;

Fig. 4 is a top sectional view of the antenna structure shown in Fig. 3; and

Fig. 5 is a schematic view of the antenna shown in Figs. 4 and 5 and the associated antenna circuit components illustrating the circuit arrangement thereof.

Referring now to the drawings and more particularly to Figs. 1 and 2 thereof, the present improved antenna system is there shown as being supported between the vertical tail fin Illa and the fuselage of an aircraft l0. Specifically, the antenna is supported at one end by a post l2 which is riveted or otherwise fixedly anchored to the vertical fin Illa. At its opposite end, the antenna is supported by an L bracket H, the base of which is riveted or otherwise rigidly mounted upon the fuselage of the craft at a point between the wings thereof.

In brief, the antenna system comprises two elongated and telescopically related tubular members I3 and M, formed of aluminum alloy or the like having low electrical resistance, and normally held fully telescoped one within the other by means of a helical biasing and retracting spring 15 which is housed within the inner tubular member l4. At its rear end, i. e. the end adjacent the vertical fin Illa of the craft, the inner tubular member 14 carries wind drag means It in the form of a wind sock Itb. This sock is mounted upon a supporting member 16a which is rigidly secured to the extendable end of the tubular member l4 by means of an assembly comprising an end plug il having a threaded projection Ila of reduced diameter for receiving the supporting member I641, a lock washer 2t and assembly nuts 2i. This plug is pin connected to the tubular member It by means of a pin 63 extending through registering openings in the plug and end walls of the member M. The pin is held in place by means of a sleeve 19 having an inwardly directed flange overlying the shouldered portion of the plug I1 and clamped against the end of the tubular member It by the supporting member 16a.

One end Hid of the biasing and retracting spring i5 is anchored within an opening formed in the inwardly directed and flattened end of the plug il in the manner best shown in Fig. 2 of the drawing. The opposite end of this spring is fixedly anchored to the bottom wall 22a of a closure cup 22 which extends into the opposite end of the outer tubular member E3. More specifically, the end I51) of the spring i5 is looped through two spaced apertures in the wall 22a and is soldered in place as indicated at 24. The cup-shaped member 22 is also provided with a flanged rim 2219 which overlies the flanged end 30 of the outer tubular member [3 and bears directly against a sealing gasket 23. Thus the left end of the outer tubular member i3 is sealed to prevent moisture and dirt from entering this member. The apertured end of the bracket H through which the end of the outer tubular member i3 extends is held rigidly assembled upon this end of the tubular member against the flange l3c by means of a rib 53b pressed outwardly from the wall of the tubular member I3 adjacent the flange l3c.

For the purpose of slidably supporting the inner tubular member i4 and of sealing the opposite end of the tube 13 against the entrance of moisture and other foreign matter, this tube is provided with a portion lBa of reduced diameter and appreciable length through which the inner tubular member i4 is slidable. The substantial contacting surfaces of the tubes l3 and I4 thus provided serve eiiectively to seal the interior of the tube i3 against the entrance of moisture, dirt and other foreign matter. Accurate alignment of the inner tube l4 coaxially with the outer tube 53 is obtained by providing a flange lea at the front end of the tube H! which is slidable along the inner surface of the outer tube IS. A rib i lb pressed out from the tube It to engage the inner surface of the tube l3 and displaced a short distance, i. e. approximately 10 inches from the flange Ma, is provided to engage the shoulder 63c along the outer tube l3, thereby to prevent the inner tube M from being completely withdrawn from the outer tube !3. This separated two point support for the inner tube prevents this tube from whipping when fully extended.

From the foregoing explanation, it will be understood that normally the spring l5 functions to maintain the inner tube l4 fully telescoped within the outer tube 53. This retracted setting of the antenna will prevail so long as a substantial wind pressure is not built up within the wind sock [6b. During flight of the craft ill, however, and when the air speed exceeds a predetermined value determined by the characteristics of the spring if, the wind pressure built up in the wind sock ltb serves to pull the inner tube l4 out of the outer tube is against the bias of the spring l5. Thus the eifective length of the antenna, which jointly comprises the two tubes l3 and i4, is increased. The extent to which the inner tube I4 is withdrawn is, of course, dependent upon the wind pressure developed within the wind sock l6?) and hence the air speed of the craft H3. In the usual small aircraft there is a Wide differential between the normal air speed at which the craft cruises and the air speed at which landings are effected. For example, many small civilian planes are available having landing speeds as low as 40 miles per hour and cruising speeds in excess of 100 miles per hour. For a craft of this charaeter, the spring I5 may be so designed that at any air speed below 50 miles per hour, the inner tube i4 is fully retracted within the outer tube l3 whereas at an air speed of 70 miles per hour, for example, the inner tube is fully extended from the outer tube to provide an antenna of maximum effective length.

Thus, it will be understood that with the described arrangement, extension and retraction of the antenna is accomplished in a fully automatic manner without any attention on the part of the craft operator. The extent of the antenna length obtainable will be realized from the fact that depending upon the size of the craft, the distance between the supporting bracket II and the post [2 may vary from 11 to 25 feet or more. Regardless of this distance, the maximum eifective length of the antenna, equal to twice the indicated distance, is developed through action of the described facilities when normal flying speed of the craft is attained.

In the second embodiment of the invention illustrated in Figs. 3, 4 and 5 of the drawings, facilities are provided for automatically obtaining still greater elongation of the antenna when the normal flying speed of the craft is attained and for automatically maintaining the antenna circuit tuned to the desired signal carrier frequency. In this modified arrangement, a flexible antenna Wire or cable 4| of conventional form is connected between a traveling pulley support 41 and wind drag means in the form of a wind sock 56. Intermediate its ends, this wire is lo'oped around a stationary pulley 42 and a traveling pulley '43, which latter pulley is spring biased away from the stationary pulley 42 by means of a helical coil spring 5!. The enumerated operating parts of the antenna, with the exception of the sock 56, are housed within a tubular metallic mem ber 36 of oval cross section having end closure assemblies at the respective ends the'reof. specifically, the left end of the tubular member 30 is closed by end closure means -which comprises a metallic plug 36 fitting within and rigidly secured to the tubular member, and stacked end plates 37 and 38 rivet connection to the plug 36 and having peripheral edges which overlie the end of the member 30. The three stack parts 36, 3'! and 38 are also drilled to receive 'a tubular ferrule 40 through which the extensible end of the antenna wire 4| may be withdrawn from the member 39 and retracted. This end closure assembly is utilized fixedly to support the stationary pulley 42. Specifically, this pulley is rotatably mounted by means of a pivot pin 45 between the legs of a U-shaped bracket 44 which is 'rivet connected at its base to the end unsure parts 36, Hand 38 by means of the assembly "rivet 39. A resilient U-shaped retaining element 46 having legs overlying the wire grove of the pulley 42 is also riveted to the base of the pulley bracket 44 to prevent the antenna wire 4| from jumping out of the pulley grove.

The opposite end of the tubular member 30 is closed by a similar end closure assembly comprising the metal parts 32., '3'3 and 34, which are held in stacked relationship by means of assembly rivets 35. The first of these parts, i. e., the part 32 is in the form of an ..-bracke't having a projecting base 32a adapted for screw, rivet. or bolt connection to a suitable insulating support carried by an aircraft along the foreward end of the craft fuselage. The described end closure parts are utilized to support a stationary contact element 52. Specifically, this element extends through an opening in the stacked parts 32, 33 and 34 and is insulated from these parts by means of an insulating sleeve 53 having an enlarged head 53a abutting the inner surface of the closure plug 33. At its projecting end the sleeve 53 supports a ferrule 55, preferably soldered to the bracket 32 and through which an insulated circuit conductor 54 may be extended for connection with the contact element 52. This contact element is provided with acontact head 52a, normally engaging the contact head 49a of a,

movable contact element 40. The latter contact element is provided with a shank driven into an opening drilled into an elongated rod 50 which is movable longitudinal of the tubular member 39. At its left end, this rod carries a pulley bracket 41 upon which the traveling pulley 43 is rotatably'supported by means of a pivot pin 48. The inner end of the antenna wire 4| is fixedly connected to an overhanging end portion 41a of the bracket 41 in the manner best illustrated in Fig. 3 of the drawings. The rod 50 and bracket 41 are also utilized to support a resilient U-shaped retaining element 49 having legs which overlie the wire groove in the pulley 43 to prevent the antenna wire 4| from jumping out of this groove. The only connection between the traveling pulley assembly, i. e., the parts 50, 43, 41, 48 and 49, and the tubular member 30 is the biasing spring 5|. This spring is telescoped over the rod 50, fixedly anchored at one end to the end closure part 33 and fixedly anchored at the opposite end to the pulley bracket 41.

For the purpose of mounting the described antenna assembly upon an aircraft, the L-bracket 32 located at one end of the tubular member 3|] and a clamping member 3| are employed. Specifically, the member 3| embraces the tubular member 30 and is provided with formed tubular parts 3| adapted for clamping engagement with the end of a post, not shown, anchored to the fuselage or tail assembly of the craft. Bolts 3|b extending through the legs of the member 3| are employed to produce a clamped connection between this member and the upstanding end of the supporting post. In mounting the assembly upon the craft, all parts thereof are insulated from the metal parts of the craft. To this end, a supporting post of insulating material is employed in conjunction with the clamping member 3| to provide support for the assembly adjacent one end thereof. Suitable insulation means are also employed in conjunction with the L-bracket 32 to insulate this bracket from the craft fuselage in mounting the bracket upon the fuselage.

With the described arrangement, the spring 5| normally holds the antenna wire fully retracted and maintains the rod 50 in a position such that the contacts 48a and 52a are engaged. When thus fully retracted, the antenna wire includes three sections 4m, Mb and Me which are available to form the antenna of the desired length. During flight of the craft and when the wind pressure built up within the sock 3| exceeds a predetermined value, the wire 4| is pulled out of the tubular member 30 through the ferrule 40 and concurrently therewith the traveling pulley 43 and the rod 5e are moved toward the stationary pulley 42 against the bias of the spring 5|. Immediately such movement of the rod 50 starts, the circuit switching contacts 40a and 520. are opened. Due to the action of the described pulley system, a ratio of two to one is provided between the rate of movement of the antenna wire and the rate of movement of the pulley 43, i. e., as the pulley 43 is moved a given distance, the antenna wire will be extended twice this distance. When normal flying speed of the craft is attained, the antenna wire is fully extended and the pulley 43 is moved to a position closely approaching the position of the stationary pulley 42. This extended setting of the antenna will prevail so long as the normal value speed of the craft is maintained. When, however, the flying speed is reduced for landing purposes or the like, the retracting spring 5| returns the traveling pu11ey'43 to its normal position as shown in Figs. 3 and 4 of the drawings. During such retracting movement of the pulley 43, the antenna wire 40 is retracted until substantially the entire length thereof is pulled back into the tubular member 39, and the rod 56 is retracted to reclose the contacts 40a and 52a.

The circuit switching contacts 52a and 40a are preferably utilized to control the tuning of the antenna circuit so that this circuit is tuned to the desired carrier frequency both when the antenna wire is retracted and is extended. Specifically, the antenna assembly including the wire 4| and the tubular member 30 is included in an antenna circuit which comprises an adjustable tuning inductor 51, a condenser 59 and an auxiliary tuning condenser 60. The identified circuit components are mounted within a shielding container 62 which is connected to ground, i. e., the fuselage of the craft, through a conductor 64. The signal input and output terminal is in the form of a jack 58 having an insulated contact 58a connected to the inductance tap 51a.

With the described circuit arrangement, the active portion of the inductor 5| and the condenser 59 comprise a series of resonant circuit effective to tune the antenna system to the desired resonant frequency. The condenser 59 is utilized as the coupling element through which signal energy is extracted from and delivered to the antenna system. A neon lamp 83 having its terminals bridging the condenser 59 and visible to the craft pilot is preferably provided to indicate that signal energy is being delivered to the antenna system during a period of signal transmission.

As will be evident to those skilled in the art, with circuit components of fixed parameters in the antenna circuit, the tuning of the circuit is changed as the antenna wire 4| is extended and retracted. To prevent this from occurring the contacts 52a. and 40a are closed when the wire 4| is retracted to bridge the tuning condenser Bil across the series resonant circuit, comprising the inductance 51 and the condenser 59, over a path which includes the conductor 54 and the conductively iconnected parts 50 and 32. With the condenser 69 thus included therein, the antenna circuit is tuned to the desired signal carrier frequency. Upon extension of the antenna in the manner explained above, the contacts 520. and 400. are opened to interrupt the described shunt path including the condenser (50, thereby to exclude this condenser from the circuit. With the antenna wire 49 fully extended, however, the antenna circuit is tuned to the same desired signal carrier frequency even though the condenser 69 is excluded therefrom. Thus it will be understood that the contacts 400. and 52a cooperate with the tuning condenser 68 to determine the signal carrier frequency to which the antenna circuit is tuned. Preferably the condenser 59 and 60 are of the adjustable or trimmer type in order to permit factory adjustment thereof and thus provide for tuning of the antenna circuit action as defined in the appended claims.

I claim: 1. An antenna system for an aircraft, comprising an elongated tubular member, an antenna element movable outward through said tubular member to an extended position, an elongated helical spring within said tubular member normally biasing said antenna element to a retracted position, and wind drag means attached to said element to move said element to an extended position against the bias of said spring only when a predetermined drag pressure is applied to said drag means, said spring being operative automatically to retract said element when the drag pressure on said drag means drops below said predetermined value.

2. An antenna system for an aircraft, comprising an elongated tubular member, means closing one end of said member, a tubular antenna element mounted within said member for sliding movement in and out of the other end of said member between retracted and extended positions, wind drag means attached to the outer end of said antenna element to move said element to its extended position in response to the application of a predetermined drag pressure to said drag means, and an elongated helical spring disposed within said antenna element and connected between said outer end of said antenna element and said closed end of said member to retract said element from its extended position when the drag pressure on said drag means drops below a predetermined value.

3. An antenna system for an aircraft, comprising an elongated tubular member, means closing one end of said member, a tubular antenna element mounted within said member for sliding movement in and out of the other end of said member between retracted and extended positions, an elongated helical spring disposed within said antenna element and connected between said outer end of said antenna element and said closed end of said member to bias said element to its retracted position, and wind drag means attached to the outer end of said element to move said element to its extended position against the bias of said spring means only when a predetermined drag pressure is applied to said drag means, said spring being operative automatically to retract said element when the drag pressure on said drag eans drops below said predetermined value.

4. An antenna system for an aircraft comprising an elongated support member, an antenna wire having an end anchored on said support member and an extendable end, a pair of relatively movable pulleys mounted on said support member over which said wire is looped, spring means secured to said support member biasing one of said pulleys away from the other, thereby to hold said wire retracted, and wind drag means attached to said extenda'ble end of said wire to pull said pulleys toward each other against the bias of said spring means and thus extend said wire when a predetermined drag pressure is applied to said drag means.

5. An antenna system for an aircraft, comprising an elongated support member, a stationary pulley mounted on said support member, a traveling pulley mounted for movement along said support member, an antenna wire anchored at one end on said support member and looped around said stationary pulley and said traveling pulley in the order named, spring means secured to said support member biasing said traveling pulley away from said stationary pulley, thereby normally to hold said wire in its retracted position, wind drag means connected to the other end of said wire to pull said pulleys toward each other against the bias of said spring means and thus extend said wire when a drag pressure is applied 8 to said drag means, and switching means operative in response to movement of said travelling pulley relative to said stationary pulley.

6. An antenna system for an aircraft, comprising an elongated tubular member, end closure means for said tubular member, an antenna wire having an anchored end within said tubular member and an extendable end extending through one of said end closures, a pair of relatively movable pulleys mounted within said tubular member and over which said wire is looped, spring means housed by said tubular member and biasing one of said pulleys away 'from the other, thereby to hold said wire retracted, and wind drag means attached to said extendable end of said wire to pull said pulleys toward each other against the bias of said spring means and thus extend said wire when a predetermined drag pressure is applied to said drag means.

'7. An antenna system for an aircraft, comprising an elongated tubular member, end closure means for said tubular member, stationary and traveling pulleys mounted within said tubular member, an antenna wire anchored at one end and looped ar and said stationary pulley and said traveling pulley in the order named, spring means housed by said tubular member and biasing said traveling pulley away from said stationary pulley, thereby normally to hold said wire in its retracted position, the other end of said wire extending through one of said end closure means, and wind drag means connected to said other end of said wire to pull said traveling pulley toward said stationary pulley against the bias of said spring means and thus extend said wire when a drag pressure is applied to said drag means,

8. An antenna system for an aircraft, comprising an elongated tubular member, end closure means for said tubular member, stationar and I traveling pulleys mounted within said tubular member, an antenna wire anchored at one end and loopedaround said stationary pulley and said traveling pulley in the order named, spring means housed by said tubular member and biasing aid traveling pulley away from said stationary pulley, thereby normally to hold said wire in its retracted position, the other end of said wire extending through one of said end closure means, and switching means operative in response to movement of said traveling pulley relative to said stationary pulley.

9. An antenna system for an aircraft, comprising an elongated tubular member, end closure means for said tubular member, a stationary pulley mounted within said tubular member at one end thereof, an elongated rod disposed within and movable longitudinally of said tubular member and provided with a contact at one end thereof, a stationary contact engageable by said firstnamed contact and supported adjacent the other end of said tube, a traveling pulley mounted upon saidrod at the other end thereof, an antenna wire anchored at one end and looped around said stationary pulley and said traveling pulley in the order named, a helical coil spring embracing said rod and connected between said rod and the end closure means at said other end of said tubular member 'to bias said traveling pulley away from said stationary pulley, thereby normall 'to hold said wire in its retracted position and said contacts in engagement, the other end of said wire extending through the end closure means at said one end of said tubular member, and wind drag means connected to said other end of said'wireto pull said traveling pulley and rod toward said stationary pulley against the bias of said spring means and thus extend said wir and disengage said contacts when a predetermined drag pressure is applied to said drag means.

10. An antenna system for an aircraft, comprising an elongated antenna element, means supporting said element for movement to an extended position, means biasing said element to a retracted position, wind drag means connected to said element to move said element to an extended position against the bias of said biasing means only when a predetermined drag pressure is exerted upon said drag means, and circuit switching means operated by said biasing means and said drag means as said element is moved between said retracted and extended positions.

11. An antenna system for an aircraft comprising an elongated antenna element, means supporting said element for movement to an extended position, means biasing said element to a retracted position, wind drag means connected to said element to move said element to an extended position against the bias of said biasing means only when a predetermined drag pressure is exerted upon said drag means, circuit switching means operated by said biasing means and said drag means as said element is moved between said retracted and extended positions, and tuning means controlled by said switching means to determine the tuning of said circuit.

12. An antenna system for an aircraft having a flying speed considerably in excess of its landing speed, comprising an extensible and contractible antenna element, an antenna circuit includ- 10 ing said antenna element and having a. resonant portion associated therewith, circuit switching means for controlling said resonant portion, and means controlled in accordance with the speed of said craft for automatically extending said antenna element when said craft attains a flying speed in excess of a predetermined speed and for automatically retracting said antenna element when the speed of said craft is reduced below said predetermined speed, said switching means being mechanically connected to said antenna element and being solely mechanically operated thereby in accordance with the longitudinal movement of said antenna element for connecting and disconnecting said resonant portion of said antenna circuit to determine the tuning of said circuit in accordance with said longitudinal movement.

DONALD H. MITCHELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,048,015 Loque July 21, 1936 2,080,539 Irvin May 18, 1937 2,157,112 Bonner May 9, 1939 2,187,575 Schroder Jan. 16, 1940 2,249,836 Lear July 22, 1941 2,251,418 Pavlik Aug. 5, 1941 2,272,213 Lear Feb. 10, 1942 2,364,637 Lear Dec. 12, 1944 2,417,191 Fox Mar. 11, 1947 

